Abstract：In the present study, the influence of Salmonella enterica serovar Typhi (S. typhi) plasmid pRST98 on autophagy of human-derived macrophage-like cell line THP-1 was investigated. THP-1 cells were infected with wild type strain (ST6), mutant strain (ST6-ΔpRST98) and ST6-ΔpRST98 with a complemented plasmid encoding pRST98 (ST6-c-pRST98), and the lysosomotropic agent chloroquine (CQ) was added for intervention. First, the appropriate concentration of CQ was determinated by detecting the influence of CQ on cells and bacteria respectively. The cells were collected at different time points after cocultivation with bacteria. The changes of protein LC3Ⅱ, p62, autophagosome and autolysosomes were detected by Western blotting and monomeric red fluorescent protein-green fluorescent protein (mRFP-GFP)-LC3 plasmid transfection. The results revealed that 30 μmol/L CQ could significantly block the autophagic process, and had no obvious influence on the cells and bacteria. The Western blotting analysis showed that the augment of autophagy protein LC3Ⅱ and p62 in ST6-ΔpRST98 group was higher than those in ST6 and ST6-c-pRST98 groups after CQ treatment. Similarly, the LC3 dots in the groups treated with CQ were higher than those in the groups without CQ treatment. Specifically, even more remarkable level of LC3 dots in ST6-ΔpRST98 group than that in the wild type group was observed. All these evidences suggested that S. typhi plasmid pRST98 works in the early stage of autophagy, prior to degradation in autolysosomes.
